The brain relies on a real-time supply of oxygen and nutrients through the microvasculature, which runs like electrical wires through nerve tissue. Modern imaging techniques allow researchers to track the activity of individual neurons in the brain, but they have not yet advanced enough to dissect microvascular function at comparable spatial scales. This gap impedes our understanding of cerebral small vessel disease and its contribution to cognitive impairment and dementia.
To address this challenge, a research team at Washington University in St. Louis and Northwestern University, led by Song Hu, professor of biomedical engineering in the McKelvey School of Engineering, developed super-resolution functional photoacoustic microscopy (SR-fPAM). SR-fPAM allows researchers to image blood flow and oxygenation in the mouse brain at single-cell resolution by tracking the movement and oxygenation-dependent color changes of red blood cells. This fills a critical gap in functional microvascular imaging and has the potential to provide new insights into microvascular health and diseases such as stroke, vascular dementia, and Alzheimer’s disease.
The research results will be published on March 3, 2026. Light: Science and Applications.
Red blood cells, which are abundant in blood vessels, naturally absorb light through hemoglobin, a molecule responsible for oxygen transport. When exposed to short laser pulses, hemoglobin emits ultrasound waves. This is a phenomenon known as the photoacoustic effect. Conventional photoacoustic microscopy can image blood vessels without labeling, but does not provide single-cell resolution in 3D.
Hu’s team addressed this limitation by developing a high-speed photoacoustic microscope that can repeatedly image the same brain region every millisecond, allowing the movement of red blood cells to be tracked in single files in capillaries and in groups in larger blood vessels. By tracking these cells over a series of frames and computationally accumulating their trajectories, the researchers were able to reconstruct 3D microvascular structures at single-cell resolution.
Similar to super-resolution fluorescence and ultrasound imaging, SR-fPAM leverages high-speed imaging to track dynamics and uses that information to identify features smaller than traditional resolution limits. Condense multiple spatiotemporally acquired frames into a single frame with significantly improved resolution. ”
Song Hu, Professor of Biomedical Engineering, McKelvey School of Engineering
In their experiments, SR-fPAM revealed how blood flow and oxygen supply are redistributed across a 3D microvascular network in the brain after an induced stroke. When a single microvessel was occluded, the flow patterns of nearby blood vessels instantly changed, allowing red blood cells to redirect and maintain oxygen supply to the affected tissue.
“If one blood vessel becomes clogged, red blood cells take another route to continue blood flow and oxygen delivery,” Hu said. “With SR-fPAM, we can observe not only structural changes in 3D microvasculature, but also how fast red blood cells move, how their direction of flow changes, and how red blood cells release oxygen to surrounding tissues in response to stroke-induced ischemia.”
Looking to the future, Hu and his team hope to combine SR-fPAM with two-photon microscopy to be able to simultaneously image both red blood cells and neurons at single-cell resolution.
“This will allow us to study how neurons and microvessels are spatiotemporally regulated and how their dynamic coupling is disrupted during disease,” Professor Hu said. “It may also help better interpret clinical neuroimaging techniques, such as functional MRI, which infer brain activity from vascular signals.
Hu said this research could have significant translational implications.
“Cerebral small vessel disease is increasingly recognized as a major cause of cognitive impairment and dementia, and WashU is at the forefront of this in both basic and clinical research,” said Hu. “A better understanding of how microvascular oxygenation and blood flow change during the early stages of disease could help develop early detection strategies and therapeutic interventions.”
sauce:
Washington University in St. Louis
Reference magazines:
Zon, F. others. (2026). Super-resolution functional photoacoustic microscopy with label-free cell tracking. Light: Science and Applications. DOI: https://doi.org/10.1038/s41377-026-02235-3. https://www.nature.com/articles/s41377-026-02235-3
